Back in the days before all figure phone numbers, London exchanges had names: when all figure numbers were introduced these used the corresponding numbers. For example, my home phone when I was a lad was Putney 6*** (PUT 6***) - this later changed to 788 6***, then 01 788 6*** etc. When local names were used up new exchanges used suitable names which were close when translated into numbers. So when the Wandsworth exchange needed to expand they used the name Vandyke; these later became 926 and 826. Many supplementary exchanges used the names of artists (Vandyke, Flaxman etc.), but the exchange for the London Bridge area had the best name of all, and was called HOP (later 467).